For evaluating or designing eyeglass lenses, various evaluation methods and designing methods are proposed to obtain the optimal visibility, and especially a technique is proposed which is focusing on eyesight in a state in which eyeglass lenses are worn. For example, in patent document 1 (WO2002/088828), a technique for designing eyeglass lenses using a vidual function is disclosed. In patent document 2 (WO2004/018988), eyeglass lenses, which are designed through considering chromatic aberrations of the visual function, are disclosed. Here, the visual function is a function representing eyesight, which is normalized with optical aberrations of the lenses and characteristics of eyeballs (relative accommodation values, relative convergence values, physiological astigmatic quantities), when viewing through eyeglass lenses (normalized eyesight such that, when corrected completely, it becomes 0 in logMAR).
However, in patent document 1 and patent document 2, a binocular function, at a time when eyeglass lenses are worn, is not considered at all. For example, in patent document 1, since the object is to apply for a general-purpose lens, individual elements, for example, such as a relative accommodation or a relative convergence are not considered. Therefore, it is not suitable for designing optimal eyeglass lenses, for which individual information regarding a binocular vision is taken into consideration. Since it is for general-purpose lenses, naturally, a design of eyeglass lenses for both eyes is not considered. In patent document 2, though it is considered with respect to a chromatic aberration portion of the visual function, for other portions, as with the above patent document 1, a technical content is insufficient for an individual design in which a binocular vision is considered.
On the other hand, in patent document 3 (Japanese Published Examined Application No. HEI02-39767B (Japanese Published Unexamined Application No. SHO57-10113A)), patent document 4 (Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2008-511033A), and patent document 5 (Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2000-506628A), there are references with respect to how it can be seen with left and right eyes, when a pair of eyeglass lenses are worn.
The invention described in patent document 3 is an epoch-making patent as an approach to a binocular function. In patent document 3, a desired condition with which the binocular function is realized is described. Namely, a range of an astigmatism in a progressive band, arrangement of an astigmatism and an alignment error in a whole of a lens, prism ranges of left and right eyeglass lenses, and a condition on directions of skews induced by the prisms are described. However, reevaluated from the present, the invention described in patent document 3 includes some defects.
Firstly, an aberration calculation of a line of fixation emitted from a lens is performed without considering the Listing's law at one eye which is a primary movement of the eyeball. In this case, the calculation of a residual astigmatism becomes uncertain, and it cannot say that there is the predetermined effect described in the document. Further, the movement of an eyeball of one eye can be considered as a rotational movement performed while centered at one point in the eyeball, that is, the center of the rotation. A frontal plane including the center of rotation at a position where the eyeball is gazing front is called a Listing's surface. It is the law of major movements of an eyeball that the rotational axis of the eyeball lies within a Listing's surface, and it is called the Listing's law.
Secondly, it is written that progressive portions of the left and right lenses are within the prism ranges, and that almost the same astigmatism and alignment errors are taken and defocuses are the same, therefore a stereoscopic vision (it seems that a binocular vision) is fine. However, in patent document 3, it is not shown that what balance of an astigmatism and an alignment error is fine for the stereoscopic vision, and the extent of fineness is not quantitatively shown. In this regard, it is not clear how the eyeglass lenses described in patent document 3 are configured.
Thirdly, on page 5, lines 25-44 of patent document 3, the explanation of “FIG. 2” of the document is not for an optical system for a binocular vision. This figure is shown in FIG. 44. In FIG. 44, when eyeballs 57 and 58 look straight at a point Pp on a subject surface 59, lines of sights 50 and 51 are directed to the point Pp. Eyeglass lenses 52 and 53 are arranged in front of the eyeballs 57 and 58. By the prism effect of the eyeglass lenses 52 and 53, for a left eye 57, it is seen that the point Pp is placed at an intersection point PL of the line of sight 54 and the surface 59, and, for a right eye 58, it is seen that the point Pp is placed at an intersection point PR of the line of sight 58 and the surface 59. It is described in lines 41-42 on the same page that the relationship between the lines of sights shown in FIG. 44 can be deemed as one eyeglass lens which is symmetrical with respect to a prime meridian. However, as it can be seen from Prentice's formula (P=(h×D)/10), a prism effect is proportional to a dioptric power. Therefore, this assertion is valid only for lenses such that the left lens and the right lens are identical.
Additionally, Prentice's formula is an approximation formula which is sufficient for ordinary use, and it means that prism P of a lens is proportional to a distance, h (in unit of mm), from the center and diopter D. In short, since optical powers of a left lens and a right lens are generally different, the above described assertion is not obvious and not established. Further, after the explanation of “FIG. 2” in patent document 3, the explanations are based on one of the left lens and the right lens throughout the document, without specifying a coordinate system and the origin that specify the target point Pp. Therefore, the configuration is not suitable for an optical system for a binocular function.
Fourth, the extent of the distortion shown in “FIG. 4” of patent document 3 is difficult to understand. This figure is shown in FIG. 45. The explanation of the figure in patent document 3 is in line 17 on right column on page 5, where it is explained that the figure is an imaging figured of an equidistant and symmetrical lattice. “FIG. 4” in this document is a figure in which, positional differences from a point P is drawn, when a grid point of the lattice is set to the point P, and especially, it can be seen that it is distorted at the lower peripheral part. In lines 25-27 on the same column of patent document 3, it is explained that this is a saddle-shaped distortion or a barrel distortion. Namely, in patent document 1, it is taught that there is a relationship between the positional differences in horizontal direction, ΔPE, and the distortion. When it is assumed that there is a relationship between the positional differences in horizontal direction, ΔPR, and the distortion, the lattice must be distorted when all the lines of sights 54 and 55 have intersection points other than the point P on the surface 59. However, in this case, since the positional differences in horizontal direction are 0, a contradiction arises in that the above described “FIG. 4” becomes a figure which is not distorted. Therefore, the positional differences in horizontal direction, ΔPR, has no relationship with the distortion. Further, it is described that a distorted figure is processed as an image drawn with straight lines by a brain. However, a basis is not described regarding, to what extent the figure is distorted, the figure can be processed as lines, though it is an important matter. Therefore, it cannot be clearly understood whether the distortion shown in FIG. 45 becomes straight lines in a brain or not.
Fifth is that the target is on the surface. Basically, the target is arbitrarily determined by a designer. Therefore, in general, eyeglass lenses are designed so that performance of the eyeglass lenses becomes higher at an arbitrarily target determined by a designer. However, in patent document 3, the evaluation method is limited to candidates of targets which are adopted for eyeglass lenses for reading characters on a tight news paper or on a wall. Points within the target other than fixation point in patent document 3 have big differences in distances from both of the eyeballs. Therefore, it becomes difficult to simultaneously adjust an error in power from the fixation point, a residual astigmatism, and prism. Consequently, the prism becomes bigger. Therefore, in a system in which the target is on a surface, it is difficult to evaluate a binocular vision.
In patent document 4, a design method for eyeglass lenses is proposed. In the design method, a state, in which a front view direction of a person wearing a pair of eyeglasses is shifted toward a side of a dominant eye, is considered. If the shift described in patent document 2 is true for a near vision, then it is an interesting phenomenon and, naturally, there should be an invention which utilizes the physiological phenomenon. However, patent document 4 includes the problems described below.
Firstly, an object to be measured is a living body. Thus, there is a problem on accuracy of measurement. In the example described in paragraph 0030 of patent document 4, it is written that the shift is 2 cm. If there is 2 cm, it is easy to measure, but if the shift is smaller, it becomes difficult to stably measure. It is described in paragraph 0063 of patent document 4 that it can be measured with “an absolute error of less than or equal to 3 mm.” However, taking into consideration that an ordinary amount of an inset for near vision in a progressive power lens is 2.5 mm, the amount of the error is very large.
The second problem is that a phenomenon that “a front view direction is shifted toward a side of a dominant eye” contradicts the Hering's law of equal innervations, which is the only one law regarding binocular eye movements. It is difficult to improve a binocular function by designing eyeglass lenses through a measure which is based on a phenomenon contradicting the Hering's law of equal innervations. Additionally, an explanation of Hering's law of equal innervations can be seen in non-patent document 15 (written by Ryoji Osaka, Sachio Nakamizo, and Kazuo Koga, “Binocular Movement and Hering Theory, Experimental Psychology of eye movement”, The University of Nagoya Press, (1993), Chapter 3, p. 60-61, written by Sachio Nakamizo). The Hering's theory regarding binocular movement consists of a hypothesis that an innervation of version (ipsilateral binocular movement), which generates binocular movement, and an innervation of vergence (contralateral binocular movement) exist, a hypothesis of equal innervations of both eyes that means amounts of innervations assigned to respective eyes are always equal (Hering's law), and a hypothesis of additivity of innervations that means additivity holds between these two types of innervations.
Further, as a different opinion, it is known that a center of rotation is not fixed and it moves as well as shifts, during ocular movement. It is known that the center of rotation does not rotate while centered by a single point, and it rotates while centered by different points depending on its use. The assertion of “shift of a front view direction” in patent document 4 can be explained from a fact that a center of rotation of an eyeball itself shifts. Namely, when it is considered that centers of rotations move, a midpoint between the centers of rotation of left and right eyeballs also moves, and a front view direction also moves. In this manner, it is considered that an assumption that left and right eyeballs symmetrically move better conforms to the physiological fact than the assumption that left and right eyeballs asymmetrically move, which is insisted by patent document 2.
Thirdly, it is written in paragraph 0039 of patent document 2 that “a superior binocular fusion is brought.” However, the extent is not clear. Specifically, it is written that if an occurred astigmatism (it is considered as a residual astigmatism) is less than or equal to 0.5 diopter, then it is a comfortable field of vision. However, an error in power occurs depending on a target distance. A comfortable field of vision is not realized, except for the case in which it is supposed that the target is placed at a position at which the error in power is 0. In an embodiment of patent document 4, two figures, which are a figure of errors in power and a figure of occurred astigmatisms, are shown depending on conditions of observations. However, their balances are not mentioned. Therefore, it can be hardly understood whether comfortable fields of vision can be obtained without showing the balances or a relationship between an error in power and an occurred astigmatism.
Further, it is incorrect to insist that “a binocular fusion becomes better” by diagrammatically showing only errors in power and occurred astigmatisms. A disorder in which a binocular vision is disabled even if left and right eyes are gaining good abilities to see can be found mainly in many squint patients. In a conventional evaluation of an error in power and an astigmatism such as the evaluation in this patent document 4, the evaluation of performances specific to binocular vision is not suitable.
Fourth, as in the case of patent document 3, the object of this patent is a surface, as it is apparent from “FIG. 1” or “FIG. 4” of patent document 4. Namely, things that are similar to the fourth indication regarding patent document 3 can be said.
In patent document 5, a technique regarding an eyeglass lens of so-called a wrap-around type, the lens being curved from its front towards an ear side, is disclosed. Further, on page 13 or page 15 of patent document 5, there are some descriptions regarding an off-axis prismatic disparity. Here, defects regarding a binocular vision, the binocular vision being the thesis in patent document 5, are mainly described.
Firstly, it is written that techniques disclosed in patent document 5 are a technique about an eyeglass lens of wrap-around type or an eyeglass lens of a protective eyewear. However, their configurations are unclear. In the main invention described in patent document 5, it is assumed that there are a prescribed area and a peripheral temporal area. The difference between these two areas lies in shapes of surfaces, as described on pages 28-30 of patent document 5. Here, a method of explaining the difference is not based on evaluations by ray tracing calculations which are commonly used at present, but it is a simplified method which calculates from a shape of a lens surface which has been used for the explanation of a progressive lens in the past. Therefore, the refractive power and the astigmatism are derived values of a curve which are calculated from derivatives of the surface. Thus they are different from those calculated by the ray tracing. Further, similarly, there is no description regarding consideration of the Listing's law of movement of an eyeball, which is usually taken into consideration for designing at present. Therefore, it is different from an evaluation or a design which is based on a physiological basis, such as the Listing's law. Further, the peripheral temporal area is so arbitrarily that the difference from the prescribed area becomes not clear. Thus the peripheral temporal area is not forming a limiting condition. Therefore, it can be considered that the description is only valid for normal design of a lens.
Secondly, regarding the definition of the off axis prismatic disparity described in a lower part of page 13 of patent document 5, it is only described that “a defect on a binocular vision arises when an astigmatism at a temporal part and an astigmatism at a nasal part are not equal.” However, the description is insufficient and it cannot be understood what astigmatisms are referred to. Further, as a method of correcting the off-axis prismatic disparity, there is only a description on page 15 of patent document 5 that an aspheric surface is adopted. Thus, the description is insufficient. In addition, though it is clear that the evaluation is performed with a single eye lens, it is concluded on page 13 of patent document 5 that “there is a defect on a binocular vision.” The ground of the conclusion is not clear.
Thirdly, on page 15 of patent document 5, an adjustment among a refractive power, an astigmatism, and a disparity of a prism, and a balance of elements for an optical correction are mentioned. However, the description that a defect on a binocular vision is acceptable as long as the defect is within a range of the values of the table on page 15 cannot be understood. It can be read from this table that a correction amount decreases as a prescribed lens power becomes stronger. It can be read that an error is sufficiently corrected with a smaller correction and the defect on the binocular vision is acceptable mean that when the prescribed lens power becomes stronger, a patient's tolerance on a binocular vision becomes greater. The assertion is difficult to understand, since it is a description of a tolerance based on single eye evaluation. With the subject matter of patent document 5, in which even a determination method of a tolerance of a binocular vision is not disclosed, it is hard to predict whether it is possible to design so that a tolerance is less than or equal to this tolerance, as with a standard of normal eyeglass lenses. Namely, it is not easy to apply this tolerance to a lens design of another general prescription, with a description of such a tolerance in a state in which even a binocular vision is not defined.
Here, it seems that the evaluation of a binocular vision through the single eye evaluation is based on a reason that a temporal portion and a nasal portion must be equal, since, when looking right, a right temporal portion is used in a right lens and a nasal portion is used in a left lens. However, this is a case where there is a precondition that a left lens and a right lens are the same, for example, as addressed in third problem of patent document 1. Such a prescription is very rare. Further, suppose a case in which it is asserted that prescriptions for a left eye and a right eye are almost the same. In this case, taking into consideration that the sensitivity limit in an angle of a sensory fusion is about 10 seconds in angle, it is difficult to capture a binocular vision with such a rough concept. Moreover, when applying to general-purpose lenses, it is problematic to apply the evaluation and the design that are based on such a tolerance, which lacks a physiological basis, to a human body, even if left and right prescriptions are not known in advance. As a result, there is a risk that it gives discomfort or it increases tiredness.